Mozilla has claimed that Windows RT "may have antitrust implications" as Microsoft is holding back APIs that are necessary for it to compete with modern browsers.
Windows RT, the edition of the operating system for devices running on ARM processors, will offer two different environments: Metro mode, which is designed for touch-based apps, and Desktop mode, which will only run on Microsoft code.
In a blog post, Mozilla's general counsel, Harvey Anderson, said that Windows RT may prohibit any browser except for Internet Explorer from running in the desktop environment, and that this would "signal an unwelcome return to the digital dark ages" as it will "restrict user choice, reduce competition and chill innovation".
In another blog, Asa Dotzler, director of Firefox, said that Microsoft was "trying to lock out competing browsers".
He added that running the Firefox browser in the Windows desktop environment was the only way that Microsoft had allowed Firefox to get access to APIs up until now.
"Running a browser in the desktop environment is the only way that Microsoft has allowed us to get access to the APIs that a browser needs to deliver modern capabilities and performance.
"A browser running exclusively in Metro does not have the APIs necessary to compete with Internet Explorer or any other modern browser," he said.
Ovum analyst Richard Edwards told Computing that access to the APIs should be at Microsoft's discretion and that the technology giant is not under the microscope of the Department of Justice or the EU law.
"As Windows is a proprietary operating system it is at Microsoft's discretion to what extent it wants to expose its application [to other browsers].
"Microsoft is not under the oversight of the Department of Justice, but there is nothing to stop firms who are affected by this from lobbying," he said.
Edwards also believed this was a strategic move by Microsoft to compete with Apple.
"Apple is dominating the tablet market and it has complete control over the browsers on the iPad and iOS devices. Microsoft's primary target is Apple, and it may well be saying that if anything is good enough for Apple it is good enough for Microsoft as well," he explained.
Edwards said that to compete with Apple, Microsoft will have to provide "a very tight, fully integrated stack in order to deliver the kind of experience that is comparable to an Apple device".
He also suggested that the biggest winners of this move could be Android.
"You could say as a consumer if you wanted choice you would go down the Android route. It presents an opportunity for Android."